Benzimidazole anthelmintics are widely used orally in aqueous suspension formulations for the control of parasitic helminths, namely round worms (nematodes), tapeworms (cestodes), or flukes (trematode). This anthelmintic group has been used in a variety of animal species including sheep, cattle, goats, deer, horses, cats, dogs, llama buffalo and poultry. Injectable preparations of benzimidazole anthelmintics are also known. Benzimidazole anthelmintic compounds are widely used in veterinary medicine. Common forms include oxfendazole, mebendazole, fenbendazole, albendazole and the probenzimidazoles febantel and netobimin, which are metabolised to benzimidazoles within the animal.
In general, these compounds are sparingly soluble in aqueous solutions although the solubility can be improved by heating the aqueous solution.
Bayer AG British Patent Specification No. 1527584, the full content of which is hereby included by way of reference, refers to the advantages of pour-on application in veterinary practice over oral treatments and additionally discloses a pour-on formulation characterised in that the active compound is dissolved, emulsified or suspended in a suitable solvent or solvent mixture which is tolerable by the skin (optionally with addition of further auxiliaries) and applied with the aid of a suitable device, eg. measuring cup or spray bottle to the skin of the animal to be treated. The active ingredients disclosed are Tetramisole and Levamisole.
Reference should also be had to the paper "Seasonal Variation and Anthelmintic Response by Cattle to dermally applied Levamisole", B. A. Forsyth et al. Australian Veterinary Journal, Vol. 60 No.5, May 1983 and "Pharmacokinetics of ivermectin after oral or percutaneous administration to adult milking goats", E. W. Scott et al., Journal Veterinary Pharmacology, Volume 13, pages 432-435, 1990.
E. R. Squibb & Sons Inc, U.S. Pat. No.4,145,433 discloses the option of topical or parenteral administration to mammalian hosts of benzimidazole dispersed in a non-toxic, non-pyrogenic acceptable carrier. In particular it discloses a solution for cutaneous administration being prepared by dissolving 327 mg of 5-(benzyl)sulfinyl!-1H-benzimidazole-2-yl! carbamic acid, methyl ester in a solution of about 4 cc xylene and 1 cc dimethyl sulfoxide. Such administrations are stated as being useful in treating infection caused by Haemonchus, Ostertagia, Trichostrongylus, Cooperia, Dictyocaulus, Nematodirus, Bunostomum, Strongyloides, Oesphagostomum, Trichuris and liver flukes at a recommended dosage of from 2.5-25 mg/kg body weight.